1. Field of the Invention
The present invention relates to an apparatus for separating a polarizable analyte from a sample using dielectrophoresis and a method of using the same. More particularly, the present invention relates to an apparatus having an improved membrane and a method of using the apparatus.
2. Description of the Related Art
Particles, which can be dielectrically polarized in a non-uniform electric field, are subjected to a dielectrophoretic (“DEP”) force when the particles have different effective polarizability from a surrounding medium, even if the dielectrically polarizable particles do not have electric charges. The motion of particles is determined by the dielectric properties, e.g., conductivity and permittivity, and not by the electric charges of the particles, which is well known in electrophoresis.
The DEP force applied to a particle is as follows:
                              F          DEP                =                  2          ⁢                                          ⁢          π          ⁢                                          ⁢                      a            3                    ⁢                      ɛ            m                    ⁢                      Re            (                                                            ɛ                  p                                -                                  ɛ                  m                                                                              ɛ                  p                                +                                  2                  ⁢                                                                          ⁢                                      ɛ                    m                                                                        )                    ⁢                      ∇                          E              2                                                          (        1        )            where FDEP is a DEP force applied to the particle, a is the diameter of the particle, ∈m is permittivity of a medium around the particle, ∈p is permittivity of the particle, Re is a real part, E is an electric field, and ∇ is a del vector operation. As shown in Equation 1, the DEP force is proportional to the volume of the particle, the difference between the permittivity of the medium and the permittivity of the particle, and the gradient of the square of the electric field intensity.
The direction of the DEP force is given by the Clausius-Mossofti (“CM”) factor:CM factor=Re[∈p*−∈m*]/(∈p*+2∈m*)  (2)
where ∈* is a complex permittivity and is given by ∈*=−i(σ/ω), where σ is conductivity and ω=2πf. When the CM factor is greater than 0, the DEP force is positive and the particle is attracted to a high electric field gradient region. When the CM factor is less than 0, the DEP force is negative and the particle is attracted to a low electric field gradient region.
As shown in Equations 1 and 2, the DEP force applied to the particle depends on the conductivity of the medium and the frequency and intensity of an AC voltage.
Meanwhile, devices for separating polarizable analytes via DEP have been developed. For example, U.S. Pat. No. 7,014,747 discloses an apparatus for dielectrophoretic separation, including a fluid flow channel disposed on a substrate, wherein the fluid flow channel is provided with fluid inlet and outlet means in fluid communication with the fluid flow channel, and wherein the fluid flow channel has a plurality of insulating structures disposed therein; electrodes in electric communication with each of the fluid inlet and outlet means, wherein the electrodes are positioned to generate a spatially non-uniform electric field across the plurality of insulating structures, and wherein the spatially non-uniform electric field exerts a dielectrophoretic force on a sample undergoing separation; and power supply means connected to the electrodes to generate an electric field within the fluid flow channel, wherein an electroosmotic flow of a fluid in the fluid flow channel is not suppressed. Using the apparatus, a spatially non-uniform electric field is created due to an insulation structure, but the insulation structure interrupts the flow of the fluid, thereby generating clogging. Also, it is difficult to actually separate a sample since a target material is only separated spatially in the vicinity of an array of the plurality of insulation structures. Accordingly, the use of the apparatus is limited to enriching the target material or detecting an enriched target material, and is not suitable for separating the target material. In addition, the apparatus cannot be used when the flow rate is high or when the amount of a sample is large.